I did ramps on hard with my Lv35 Apprentice, and it's stupid easy.
From what I can gather, the easiest stat build is:
70% of your total Points into Tower Attack and the remaining 30% split (15% in each) Tower Range and Speed.
Next is covering the 3 ground choke points.
Choke #1
2 blockades, Have them spaced, one behind the other. (Deals with Orge, until you're gear is better.)
2 Flame Towers behind your Blockades
1 Lightning Tower
If you're still having Orge troubles, you can either upgrade these towers to lv2, or compenstate and use 3 Flame Towers. Although, 3 should be overkill.